Presently, motors are used for a variety of information appliances, household appliances and industrial appliances, and various methods for controlling motors have been proposed.
(1) One method for controlling a motor is PWM (pulse width modulation). In PWM control, which is also called “pulse width modulation control,” the power that is input into the motor is controlled by arbitrarily changing the width of pulses of a predetermined voltage, during which electricity is supplied.
Furthermore, in general, when a motor turns, a counter electromotive voltage corresponding to the rotation speed is generated inside the motor.
If the motor is controlled by PWM control, then it is an important issue how a high-precision control can be achieved in consideration of the influence of the counter electromotive voltage generated inside the motor in correspondence to the rotation speed of the motor.
(2) One method for controlling a motor is a motor control method, in which driving of the motor is started with an initial driving signal, the rotation speed is sequentially increased by successively adding a predetermined value to the value of the initial driving signal while driving the motor with a driving signal whose signal value is set to that value obtained as a result of successive addition, and when the rotation speed has reached a predetermined rotation speed, the motor is feedback controlled by a control system having an integration means. There is furthermore the motor control method, in which driving of the motor is started with an initial driving signal for letting a gear provided on the motor shaft abut against an engaged gear that engages that gear, and after the motor is driven with a driving signal of a signal value that is larger than the initial driving signal, the rotation speed is sequentially increased by successively adding a predetermined value to that signal value while driving the motor with a driving signal whose signal value is set to that value obtained as a result of successive addition, and when the rotation speed has reached a predetermined rotation speed, the motor is feedback controlled by a control system having integration means.
If the motor is controlled by such a motor control, then the time until the motor has reached a predetermined rotation speed will vary depending on the driving load of the motor if the initial driving signal or the like is set to a constant value regardless of the driving load of the motor. That is to say, if the driving load of the motor is small, then the predetermined rotation speed will be reached in a short period of time, and on the contrary, if the driving load of the motor is large, then a long period of time will be needed to reach the predetermined rotation speed.
(3) A variety of motors are used at present for various kinds of information appliances, household appliances and industrial appliances. Among these motors, electromagnetic motors have a wiring resistance inside the motor, so that if one lets the motor rotate continuously, the motor will heat up. If the motor heats up and reaches a temperature outside the range in which proper operation is guaranteed, then there will be a risk that the motor will be damaged. To address this problem, operation of the motor is halted for a while when the motor becomes hot due to the generated heat, and cooling of the motor is performed.
However, the heating of the motor differs depending on the driving load of the motor. That is to say, when the driving load of the motor is large, then the amount of heat generated by the motor will become large, whereas if the driving load of the motor is small, the amount of heat generated by the motor will be small.
Consequently, if operation of the motor is halted when the total rotation amount of the motor has reached a predetermined amount, regardless of the driving load of the motor, then, if the driving load of the motor is small, the motor will be halted even though it would be possible to continue operating the motor, and conversely, if the driving load of the motor is large, there will be a danger that the motor will be operated in a state in which the guaranteed operating temperature of the motor is exceeded.
(4) Motors are used at present for various kinds of information appliances, household appliances and industrial appliances, and also, a variety of control devices for motors have been proposed. One such motor control device is a motor control device controlling the motor by PWM control with a control system having an integration means.
In this motor control device, to recognize the load state of the motor, a so-called measurement is performed, wherein the motor is rotated at a certain rotation speed and the output value of the integration means at that time is detected. Recognizing the load state of the motor with this measurement is advantageous with regard to speed control and position control of the motor.
However, the output value of the integration means that is attained with this measurement is not the absolute value of the load, and should rather be termed a value corresponding to the load.
There are individual differences among motors, and the counter electromotive voltage coefficient, resistance values, etc. take different values for each motor. Thus, errors occur when calculating the value of the current flowing through the motor by indiscriminately using the counter electromotive voltage coefficient and resistance value of a predetermined motor, based on the output value of the integration means obtained by a measurement at a certain load state.
Consequently, in order to perform control with regard to the absolute motor load, that is, the current actually flowing through the motor, it is necessary to convert the output value of the integration means obtained by measurement to the absolute load value (current value), giving consideration to the individual differences among motors. It should be noted that, as an example of control with regard to the absolute motor load, that is, the current actually flowing through the motor, motor heating control or the like with regard to the current value flowing through the motor can be given.